The objective of this proposal are to design, construct and evaluate ultrasonic tissue-equivalent phantoms of the breast. The purpose of the work is to create standardized objects with realistic acoustic structures and targets for assessing imaging capabilities of state-of-the art ultrasonic breast scanning equipment. Phantoms will be constructed using tissue equivalent gels for mimicking various breast constituent tissues. Designs for phantoms are based upon anatomical sections of breast tissue, available in our laboratoy as well as in the literature. Further developmental work of the phantom material is proposed, primarily in order to match small particle scattering with scattering observed in breast tissues. A major portion of the effort is devoted to the development of construction techniques for the incorporation of structures of sufficient geometric complexity to provide acoustic interfaces and mimicked tissue volumes which are representative of those encountered in vivo. Evaluation of phantoms is being carried out in part in laboratories where advanced ultrasonic breast imaging systems are being designed and employed.